Wireless data links can be unreliable. In wireless links, fading and shadowing amongst other causes can cause the wireless signal, and hence the corresponding data rate of the transmitted signal, to vary depending on events such as movements of animate and inanimate objects in the environment. The quality of data transmission may vary over space and time.
The variation and lack of reliability in data transmission may cause problems for multimedia streaming applications by causing a sudden decrease in link capacity which causes noticeable artifacts observable by the viewer of the multimedia stream. If such changes in link capacity could be predicted, it would be easier for the multimedia source to change its output data rate to match the expected change in link capacity, since the multimedia source would have more time in which to make the output rate change.